The present invention relates to a sewing machine of the double chain stitch type and more particularly pertains to the lower stitching instrumentalities thereof for forming such a stitch.
Sewing machines of this type, that are well known generally include at least one needle and cooperating looper with each having an independent thread source for the formation of seaming stitches. Such machines also include separate actuating mechanisms for the needle and looper. The one for the needle provides a means for moving the needle alternately in two senses along a rectinlinear path which is substantially vertical and perpendicular to the direction of the seam. The actuating mechanism for the looper provides a means for moving said looper along a substantially elliptical pathway which is arranged horizontally perpendicular with respect to both the axis of sewing and the pathway through which the needle travels. Additionally such machines also include conventional feeding means for advancing a workpiece through the sewing zone where the needle and looper elements perform their intended function. In known sewing machines of the type described above, the actuating means for the looper consists of two separate and similar mechanisms.
One of these mechanisms serves to provide the looper with an alternating to and fro movement which is perpendicular to the sewing axis and which substantially intersects the pathway through which the needle travels.
The other mechanism serves to provide the looper with an alternating to and fro movement which is parallel to the sewing axis and the combination of both movements causes the looper to travel in an elliptical pathway so that it will first grasp a loop of thread carried by the needle and then subsequently form a so-called "triangle of threads" into which the needle decends to effect the drawing of the looper thread through the loop of needle thread.
This mode of operation of the looper is well known to those conversant in the art and is effective in forming a double chain stitch of the type which is identified by numeral 401 in the United States Federal Standard Catalog. To form a stitch of the above described type with known devices of the prior art it is necessary that the looper also be caused to move in a direction parallel to the direction of the sewing axis in order to effect the formation of a triangle of threads which is formed by the looper itself, which forms its base, by the thread carried by the looper which is stretched between the ends thereof and the last stitch formed of the seam, as well as by the loop of thread taken from the needle that extends between the last stitch and the blade of the looper.
The latter two elements of thread form the sides of the triangle of threads with the vertex thereof being united with the workpiece so that the triangle lies extended in the direction in which said workpiece is caused to advance during the sewing cycle.
Displacement of the looper parallel to the direction of the sewing axis is provided in order to allow the looper to grasp the loop of needle thread as the needle is moving upwardly and, as is know, is located on that side of said needle at which the seam is being displaced. When the needle is raised the looper moves to a position which when said needle decends will be on the opposite side thereof and facilitates penetration of said needle into the triangle of threads during its downward travel.